1. Field of the Invention
The present invention relates to a polymer SP (station post) insulator used in support of electric power devices such as bus bar and disconnecting switch.
2. Description of the Related Art
For supporting electric power devices such as bus bar and disconnecting switch at a substation, hitherto, porcelain-made SP insulators have been mainly used, but recently polymer SP insulators are also used as disclosed in Japanese Patent Application Laid-Open No. 1999-312421. The polymer SP insulator is a support insulator formed by covering the outer periphery of FRP core with a rubber sheath having a shell and a plurality of sheds, and crimping metal-end-fittings to upper and lower ends of FRP core, and it is excellent in quake resistance, and there are its needs in quake-stricken regions and nations.
To be used as support insulator, the polymer SP insulator is demanded to have a high dimensional precision. For example, according to the ANSI standard of the United States where polymer SP insulators are highly demanded, for a polymer SP insulator of overall length of 30 inches (762 mm), the overall length tolerance is within +/−0.8 mm, the parallelism is within +/−0.8 mm, and the eccentricity is within +/−3.2 mm. FIG. 1 shows methods of measuring overall length h, parallelism p, and eccentricity e. The parallelism p is defined as the difference of highest point and lowest point of reference circle of bolt circle diameter at upper end of insulator, and the eccentricity e is defined as deviation of center point of upper and lower ends.
As mentioned above, the polymer SP insulator is formed by crimping metal-end-fittings to upper and lower ends of FRP core. At the time of crimping, deviation or elongation occurs in the metal-end-fittings. Or when cutting the FRP core, fluctuations occur in the cutting length. Due to these reasons, it is not easy to satisfy the strict requirements of overall length tolerance of SP insulator, such as overall length tolerance of ANSI standard.
The metal-end-fitting is an integrally cast part consisting of tubular parts crimped to the upper and lower ends of FRP core and a flange formed at the end, and when the tubular parts are crimped inside at two opposite positions, the crimping effect causes the elongation of the tubular part in axial direction, and the flange may be warped and deformed as shown by exaggeration in FIG. 2. Accordingly, as for the parallelism and eccentricity tolerance, too, it is not easy to settle within the strict tolerance of SP insulator such as ANSI standard.
It is hence an object of the invention to present a polymer SP insulator capable of suppressing the overall tolerance within the ANSI standard requirement etc. in a structure formed by crimping metal-end-fittings to upper and lower ends of FRP core, and also suppressing the parallelism and eccentricity by deformation of flange within the ANSI standard requirement etc.